This disclosure relates to a process for the processing of a work piece by means of electrical discharge, whereby the processing is carried out with at least two wire electrodes (so-called xe2x80x9cmultiple wire processingxe2x80x9d), and corresponding wire erosion machines.
In electrical discharge wire cutting machines, the form of the work piece to be manufactured is produced through the fact that the wire electrode and the work piece are moved against one another in such a manner that the desired contour (determined in the numeric control (NC) program) is brought about. The wire electrode is an endless wire which is continuously guided past the work point, and is thereby renewed continuously. For the specific processing goals that are to be achieved (precision, surface characteristics of the cutting surface, etc.), the processing is highly dependent upon the wire electrode that is used. Thus, it is often suitable to use different wire electrodes during a more complex processing. Different processing processes can be optimized in regard to the erosion process through the specific selection of different electrode types, or else different geometries can be simply cut. On conventional wire eroding machines, it is possible to carry out different work steps with different wire electrodes. For this, however, the operator must replace the wire supply spool manually and call up the program with suitable technology parameters. Processing with several types of wire has, therefore, previously been an exception. The specific processing task was, in general, carried out with one single wire. Wire eroding machines with an automatic wire changing device, such as disclosed in the Japanese patent disclosure document JP 56-069037, for example, have already been known for a number of years, however. One evident advantage of such a wire eroding machine lies in its increased autonomy. Thus, different types of wire can be used for the processing of the work piece within the framework of an unintended processing. Through the automatic changing of the wire, the processing time, and also the manufacturing costs as well, are thereby reduced.
There are various reasons that can lead to the choice of one of the types of wire, but the most important criterion for the decision is the smallest internal radius (rImin.) of the contour to be cut. This results from the sum of half the diameter of the wire and the width of the spark gap, as follows:                               r                      1            ⁢            min                          =                              d            2                    +                      s            gap                                              (        1        )            
It follows from this, on the other hand, that the wire diameter, with the smallest internal radius determined, must be selected as follows:
d=2xc2x7(r1minxe2x88x92sgap)xe2x80x83xe2x80x83(2) 
The use of an automatic wire changing device and of various wire electrodes within the framework of combined processing poses new problems, however, particularly in regard to the effect on the contour to be cut. In this connection, U.S. Pat. No. 5,237,145 describes a wire eroding process in which a first wire electrode from a multiplicity of wire electrodes standing ready on a wire supply roller is selected. The wire electrode thus selected is wound up. The electrical discharge processing is started. The first wire electrode is replaced by a second wire electrode with a different diameter, and an adjustment of the contour to be cut and of the width of the spark gap is carried out for the second wire electrode. The adjustment of the contour is an offset correction, carried out transversely to the specific cutting direction, that is determined by the different wire diameters. The entire contour is also xe2x80x9creducedxe2x80x9d or xe2x80x9cenlargedxe2x80x9d correspondingly. No more comprehensive corrections are known from this publication, however.